1. Field of the Invention
The present invention relates to a substrate for an inkjet print head for conducting printing on a print medium by ejecting ink according to an inkjet method, an inkjet print head having the substrate, a method for manufacturing the inkjet print head, and an inkjet printing apparatus.
2. Description of the Related Art
There is conventionally known an inkjet print head including liquid chambers and heating resistors near the liquid chambers wherein film boiling is caused in ink in the liquid chamber by heat generated by energizing the heating resistors, and the energy of a generated bubble causes the ink in the liquid chamber to be ejected.
At the time of printing, the heating resistors of the above inkjet print head are occasionally affected by physical action such as the impact of cavitation caused by bubble generation, shrinkage, and disappearing in ink and/or the chemical action of ink. In order to protect the heating resistors from the physical action and the chemical action, an upper protection layer is disposed to cover upper portions of the heating resistors.
This upper protection layer is disposed at a position to be in contact with ink. Further, since the upper protection layer is formed above the upper portions of the heating resistors, the temperature of the upper protection layer rises instantly. In such a severe environment, the upper protection layer is normally likely to corrode. Accordingly, the upper protection layer is formed with a material which has excellent resistance to the physical action and the chemical action such as impact resistance, heat resistance, and corrosion resistance. More specifically, the upper protection layer is formed with a metal film of Ta (tantalum), a platinum group element Ir (iridium) or Ru (ruthenium), or the like satisfying the above conditions.
Incidentally, these materials are conductive. In a case where a current flows through the upper protection layer, an electrochemical reaction occasionally occurs between the upper protection layer and ink, thereby damaging the function of the upper protection layer. In order to prevent this, an insulating layer (a protection layer having electrical insulation properties) is disposed between the heating resistors and the upper protection layer so that a current supplied to the heating resistors does not flow through the upper protection layer.
In such a configuration, there is a case where a short circuit occurs for some reason and a current directly flows from the heating resistors or wiring connected thereto to the upper protection layer. In a case where the short circuit causes the current to flow through the upper protection layer, an electrochemical reaction between the upper protection layer and ink occasionally occurs in a region through which the current flows, thereby degenerating the upper protection layer.
In order to prevent the short circuit from degenerating a large portion of the upper protection layer, it is considered effective to provide the upper protection layer such that in a case where the short circuit occurs, the region of the upper protection layer in which the short circuit occurs can be electrically separated from the other region.
Japanese Patent Laid-Open No. 2001-080073 discloses that in order to protect constituent elements of an inkjet print head from electrostatic discharge, a plurality of tantalum layers disposed to individually cover heating resistors are connected via fuse elements each of which is blown in a case where the corresponding heating resistor is damaged.